If you won't need to do many other numerical operations and you have a reason for preferring the data to reside in str format, you can always use the native Python min and max operating on a plain list of your data:

In general, this isn't a good way to handle numerical data and could be susceptible to many faulty assumptions about what resides in your array. But it's just another option to consider if you need to or if you have a special reason for working with strings (such as, you're only ever calculating the min and max and all you do with them is display them).

Also, you shouldn't need to convert to a list in order to use the builtin min function. I'd be shocked if it couldn't iterate over a numpy array properly.
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mgilsonJan 30 '13 at 19:17

@mgilson I agree that this would require some (probably poor) assumptions. That's why I said so in my answer.
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Mr. FJan 30 '13 at 21:31

@mgilson Yes, min would work on a flattened NumPy array, but if it's two-dimensional, even if one of the dimensions has size 1, it doesn't work. Whether someone wants to assume the arrays are flattened is up to them, but with tolist() it will definitely work. If you use tolist() on a 2-dimensional array, then min will give you the column-wise mins.
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Mr. FJan 30 '13 at 21:34